1. Field of the Invention
The present invention relates to an improved boiler apparatus, systems incorporating the boiler apparatus and to methods for making and using the boiler apparatus and systems incorporating the boiler apparatus.
More particularly, the present invention relates to an improved boiler apparatus, systems incorporating the boiler apparatus and to methods for making and using the boiler apparatus and systems incorporating the boiler apparatus, where the boiler apparatus includes a vapor removal unit that remove vapor as it boils so that the boiling throughout boiler's length remains substantially nucleate boiling.
2. Description of the Related Art
In several processes and especially in power systems using multi-component working fluids, it is necessary to completely vaporize such multi-component fluids. However, it is, in practice difficult to completely vaporize such multi-component fluid.
When a working fluid in the form of a saturated liquid is sent into a boiler, and the quantity of vapor in the stream of working fluid is relatively small, the boiling process is characterized as nucleate boiling. Nucleate boiling has a very high film heat transfer coefficient, but as vapor accumulates, a so-called crisis of boiling occurs. This crisis of boiling results in a drastic fall or reduction in the film heat transfer coefficient.
On the other hand, when a single-component fluid is vaporized, the liquid can be recycled within the heat exchanger and nucleate boiling can be sustained throughout the entire process. But, such an approach cannot be used with multi-component fluids, because the vapor produced will have a different composition (enriched by the low boiling component) than the remaining liquid resulting in a continuous composition profile across the heat exchanger with the concurrent crises of boiling.
Thus, if a multi-component fluid needs to be vaporized fully, the in a significant proportion of this vaporization process, i.e., inside the heat exchanger or boiler, nucleate boiling cannot be maintained. Thus, the film heat transfer coefficient in such a process is very low. This results in a very large increase in the required surface of the heat exchanger or boiler.
If complete vaporization of a multi-component working fluid has to be performed at high temperature, e.g., in a furnace of a power plant, then the inability of the process to maintain nucleate boiling inside heat transfer tubes of the furnace makes such a process technically very difficult.
When nucleate boiling is maintained, due to a high film heat transfer coefficient, the temperature of the metal of the heat transfer tubes is maintained close to the temperature of the boiling fluid, and as a result the tubes are protected from burn out. However, because in the process of direct vaporization of multi-component working fluids where nucleate boiling cannot be maintained, the heat transfer tubes can achieve unacceptably high temperatures resulting in tube damage or destruction.
Thus, there is a need in the art for process and apparatus for boiling and vaporization of multi-component fluids designed to achieve the production of vapor of the same composition as the composition of the initial multi-component liquid, and at the same time, to maintain a process of nucleate boiling in the heat transfer apparatus.